"Days of Future Past" bridges the gap between the 2011 prequel and "X-Men: The Last Stand," featuring the Marvel mutants traveling through time to change a major historical event that could globally impact man and mutant kind. As one of Singer's previous tweets suggested, the Vietnam War -- and now, mutants' participation in it -- will be a pivotal plot point in the May 23 release.

A large majority of recognizable faces are set to return, including Hugh Jackman, Halle Berry, Anna Paquin, Ian McKellan, Patrick Stewart, Shawn Ashmore, Ellen Page, and James Marsden reprising their respective roles in the franchise. "First Class" stars Jennifer Lawrence, Nicholas Hoult, Michael Fassbender, and James McAvoy return as the younger versions of prominent X-Men characters.